Devices with optical gain in silicon

ABSTRACT

A photonic device includes a silicon semiconductor based superlattice. The superlattice has a plurality of layers that form a plurality of repeating units. At least one of the layers in the repeating unit is an optically active layer with at least one species of rare earth ion.

CROSS REFERENCE TO RELATED APPLICATION

[0001] This application is a continuation of U.S. Ser. No. 09/924,392filed Aug. 7, 2001, which application claims the benefit of U.S.provisional application Ser. No. 60/223,874, filed Aug. 8, 2000, bothapplications of which are fully incorporated herein by reference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of Use

[0003] This invention relates generally to optical switching methods andapparatus, and more particularly to optical switching methods andapparatus that achieve optical gain in silicon.

[0004] 2. Description of the Related Art

[0005] Communication networks increasingly rely upon optical fiber forhigh-speed, low-cost transmission. Optical fibers were originallyenvisioned as an optical replacement for electronic transmission media,such as high-speed coaxial cable and lower-speed twisted-pair cable.However, even high-speed optical fibers are limited by the electronicsat the transmitting and receiving ends, generally rated at a fewgigabits per second, although 40 Gb/s systems have been prototyped. Suchhigh-speed electronic systems are expensive and still do not fullyexploit the inherent bandwidth of fiber-optic systems, measured in manyterabits per second.

[0006] All-optical transmission systems offer many intrinsic advantagesover systems that use electronics within any part of the principaltransmission path. Wavelength-division multiplexing (WDM) electronicallyimpresses different data signals upon different carrier frequencies, allof which are carried by a single optical fiber. The earliest WDM systemsdid not provide optical switching but only point-to-point WDM.

[0007] To achieve optical gain in a semiconductor metal-organic chemicalvapor deposition (MOCVD) and molecular beam epitaxy processes have beenused to produce complex nanostructures of layered materials such asInGaAs, InGaAsP and InGaAsN. These direct band gap semiconductormaterials belonging to group III and V columns of the periodic table ofelements are well known sources for LEDs, Lasers, and opticalamplifiers. However, these materials make inferior quality highsensitivity photon detectors at fiber communication wavelengths.

[0008] It would be desirable to have silicon based lasers, LEDs andoptical amplifiers because such devices would help to resolve thedifficulties of integrating optical and electronic functions on a singlechip. The high thermal conductivity of silicon can result in operationaladvantages. However, up to now efforts to obtain silicon based LEDs,lasers and amplifiers, especially devices that operate at wavelengthsfrom about 1.3 or 1.5 μm, have not been successful.

[0009] There are currently three common methods of doping rare-earthions into a silicon lattice. These methods are, (i) doping by growth ofamorphous material from a silicon/rare-earth compound, (ii) doping bychemical vapor deposition and (iii) ion-implantation and rapid thermalanneal.

[0010] The potential of utilizing rare-earth ions in a semiconductormatrix for the development of LED's and lasers, has been reported by H.Ennen, et al., Applied Physics Letters, Vol. 43, page 943 (1983). It hasalso been observed that the presence of oxygen in erbium-doped siliconcan increased erbium photoluminescence, P. M. Favennec et al., JapaneseJournal of Applied Physics, Vol. 29, page L524, (1990)].

[0011] Attempts to produce optical gain by the use of rare earths or theinclusion of materials in silicon have also been disclosed in U.S. Pat.Nos.: 5,646, 425; 5,119,460; 4,618,381; 5,634,973; 5,473,174; and5,039,190.

[0012] However, efforts to create a commercially viable silicon basedrare-earth doped LED, laser or optical amplifier have not beensuccessful due at least in part to the fact that the observedluminescence has been too weak to support such a device. Even when weakgain was observed, the radiative lifetimes measured were six orders ofmagnitude longer than those exhibited by InGaAs devices, making thedoped or implanted silicon structures inadequate for telecommunicationapplications.

[0013] There is a need for silicon based, rare-earth containing, opticaldevices that have sufficient luminescence and strong gain. There is afurther need for silicon based, rare-earth containing optical devicesthat can switch the separate WDM.channels, carrier frequencies, indifferent directions without the necessity of converting optical signalsto electronic signals. There is yet a further need for silicon based,rare-earth containing optical devices that are integrated on the samemonolithic chip as associated support circuitry. Yet there is anotherneed for silicon based, rare-earth containing optical devices thatamplify and/or attenuate light in preferred telecommunicationswavelengths, including but not limited to 1250 to 1650 nm. Still thereis a further need for silicon based, rare-earth containing opticaldevices that use avalanche multiplication effects of silicon coupledwith sufficient optical gain due to the presence of an optically activerare-earth ion.

SUMMARY OF INVENTION

[0014] Accordingly, an object of the present invention is to providesilicon based, rare-earth containing optical devices that havesufficient luminescence and strong gain.

[0015] Another object of the present invention is to provide siliconbased, rare-earth containing optical devices that have high rare-earthcontaining ion densities.

[0016] Another object of the present invention is to provide siliconbased, rare-earth containing optical devices that can switch theseparate WDM channels, carrier frequencies, in different directionswithout the necessity of converting optical signals to electronicsignals.

[0017] Still another object of the present invention is to providesilicon based, rare-earth containing optical devices with ion densitiesof at least 10²⁰ ions per cubic cm.

[0018] Yet another object of the present invention is to provide siliconbased, rare-earth containing optical devices with high densities ofoptically activated tri-valent rare earth.

[0019] Yet another object of the present invention is to provide siliconbased, rare-earth containing optical devices with silicon-based crystalfield engineering to control the symmetry of the atoms comprising thesuperlattice.

[0020] Yet another object of the present invention is to provide siliconbased, rare-earth containing optical devices with high densities ofoptically activated tri-valent rare earth.

[0021] A further object of the present invention is to provide siliconbased, rare-earth containing, periodic superlattice optical devices.

[0022] Yet another object of the present invention is to provide siliconbased, rare-earth containing optical devices that are integrated on thesame monolithic chip as associated support circuitry.

[0023] A further object of the present invention is to provide siliconbased, rare-earth containing optical devices that amplify and/orattenuate light in preferred telecommunications wavelengths, includingbut not limited to 1250 to 1650 nm.

[0024] Another object of the present invention is to provide siliconbased, rare-earth containing optical devices that use avalanchemultiplication effects of silicon coupled with sufficient optical gaindue to the presence of an optically active rare-earth ion.

[0025] These and other objects of the present invention are achieved ina photonic device with a silicon semiconductor based superlattice. Thesuperlattice includes a plurality of layers that form a plurality ofrepeating units. At least one of the layers in the repeating unit is anoptically active layer with at least one species of rare earth ion.

BRIEF DESCRIPTION OF THE DRAWINGS

[0026]FIG. 1(a) is a perspective view of a superlattice structure of thepresent invention illustrating one embodiment of a crystallinestructure.

[0027]FIG. 1(b) is a perspective view of a superlattice of the presentinvention illustrating an erbium trivalent ion inside an active regionlayer that generates a crystal field.

[0028]FIG. 2(a) is a cross-sectional view of one embodiment of aphotonic device of the present invention with silicon monolayers, erbiumatoms and crystal growth modifiers.

[0029]FIG. 2(b) is a close up, cross-sectional view of one embodiment ofthe superlattice of the present invention that is grown on a(111)-orientated surface.

[0030]FIG. 2(c) is a top down perspective view of one embodimentillustrating a superlattice of the present invention with an erbiumlayer, a silicon layers below and above the plane of the erbium layer.

[0031]FIG. 2(d) graphically illustrates a prior-art inter-bandtransition band between conduction and valence bands, compared to anintra-band transition of the present invention, with a threedimensionally confined quantum well structure that behaves as a truequantum dot.

[0032]FIG. 3 is a schematic diagram of an embodiment of an opticaldevice of the present invention electrodes and a core structure that caninclude alternating layers of silicon or silicon based compositions andrare earths.

[0033]FIG. 4(a) is a perspective view of an switch embodiment of thepresent invention.

[0034]FIG. 4(b) is a perspective view of an all optical multiplexer ofthe present invention.

[0035]FIG. 5 is a schematic diagram of an N×N optical cross-connectembodiment of the present invention.

[0036]FIG. 6 is a schematic diagram of a wavelength router/selectorembodiment of the present invention.

[0037]FIG. 7 is a cross-sectional diagram of an optical receiverembodiment of the present invention.

[0038]FIG. 8 is a cross-sectional diagram of an edge-emitting laserembodiment of the present invention.

[0039]FIG. 9 is a cross-sectional diagram of a VCSEL embodiment of thepresent invention.

[0040]FIG. 10 is a cross-sectional diagram of one embodiment of achirped superlattice of the present invention.

[0041]FIG. 11 is a cross-sectional diagram of one embodiment of achirped superlattice of the present invention.

[0042]FIG. 12 is a perspective view of a transceiver embodiment of thepresent invention.

[0043]FIG. 13 is a perspective view of an optical router of the presentinvention.

[0044]FIG. 14 is a perspective view of a wavelength converter embodimentof the present invention.

[0045]FIG. 15 is a perspective view of a parametric non-linear opticalelement of the present invention.

[0046]FIG. 16 is a perspective view of a quasi-phase-matched nonlinearelement embodiment of the present invention.

[0047]FIG. 17 is a perspective view of an all optical add-dropmultiplexer embodiment of present invention.

[0048]FIG. 18 is a schematic diagram of a two-dimensional photonicbandgap (2D-PBG) structure embodiment of the present invention.

[0049]FIG. 19 is a schematic diagram of a selectable wavelength add/dropmultiplexer embodiment of the present invention with a concentric ringwaveguide ring.

[0050]FIG. 20 is a perspective view of an optical integrated circuitembodiment of the present invention.

DETAILED DESCRIPTION

[0051] Referring now to FIGS. 1(a) through2(d), in one embodiment of thepresent invention a photonic device 10 is a silicon based superlattice11. Superlattice 11 includes a plurallity of individual layers 12 thatform a plurality of repeating units 14. At least one of layer 12 is anactive region layer 16 with at least one rare earth ion. FIG. 1(b)illustrates one embodiment of superlattice 11 with an erbium trivalention inside active region layer 16 that generates a crystal field.

[0052] Preferably repeating units 14 are periodic. At least a portion ofactive region layer 16 can be a narrow or a wide band gap semiconductor.This can be achieved when the rare-earth ion is grown as part of anarrow band gap silicon-based material or when the rare-earth ion isintroduced into the material effectively to make the material a narrowband gap material. Photonic device 10 can be an LED, amplifier, laser,photodetector, AWG, modulator, phototransistor, quantum logic gate,photonic bandgap structure, FET, MOSFET, HFET, HBT, waveguide, and thelike.

[0053] In one embodiment, superlattice 11 includes at least oneamorphous layers 12. In another embodiment, at least one of the layersin at least one repeating unit 14 has an amorphous layer 12. At leastone crystal growth modifier can be included in an individual layer 12 ofeach repeatin unit 14. Suitable growth modifiers include but are notlimited to C, As, P, B, H, O, N, Sn, Pb and the like. Additionally,during the deposition of each layer 12, additional iso-elctronic centerscan be added, including but not limited to oxygen, nitrogen and thelike, to enhance or activate the rare-earth and control the depositiongrowth or surface structure of the atoms (i.e., the reconstruction).

[0054] Photonic device 10 can be a component in a telecommunicationsystem. In various embodiments, photonic device 10 can produce opticalgain to drive a laser emission at a preferred wavelength, for example1500 to 1650 nm, amplify an incident optical signal, overcome opticallosses of other system elements, or detect a optical signal at apreferred wavelength.

[0055] Photonic device includes a superlattice that can be made of avariety of different layers and combinations thereof, 12 including butnot limited to, silicon, silicon germanium, silicon oxide, oxygen-dopedsilicon, RE-doped silicon, rare earth silicates (Re_(x)Si_(1-x)), rareearth silicon germanium (Re_(x) (SiGe )_(1-x)) and the like.

[0056] In one embodiment, superlattice 11 consists of dissimilarmaterials of type A, B and C in repeating units 14, for example, of thetype (ABA . . . ABA), or (ABCABC . . . ABC). The number and compositionof repeating units 14 is determined by the rare-earth ion interactioncross-section or density required; i.e., to increase interactioncross-section, either the number of layers is increased, or the rareearth density in each active layer is increased, or a combination ofboth. The density of the rare-earth ion is determined by thestoichiometry of the layer 12 which includes the rare-earth ion. Anotherembodiment is an ABCABC layer sequence with dissimilar materials A, B,and C.

[0057] Oxygen is an electronegative atom and very efficient in bondingthe rare-earth into a trivalent state. Therefore, oxygen doped siliconor silicon-based silicides are useful as component layers ofsuperlattice 11. In one embodiment of the ABA repeating unit 14 layersequence, the A layer is an oxygen deficient erbium silicide,represented as Er_(x)Si_(1-x) material, or an erbium containingsilicon-germanium material , represented asEr_(x)(Si_(y)Ge_(1-y))_(1-x). The B layer is an oxygen containingnon-stoichiometric or stoichiometric silicon-based material such asSiO_(x), SiGeO_(x), or oxygen-doped silicon.

[0058] In one specific embodiment, layer A is an erbium containingsilicon-based layer that is oxygen deficient; layer B is a silicon-richerbium and oxygen deficient material layer; and Layer C is an oxygencontaining silicon-based layer deficient of rare-earth ions. In thisparticular structure the erbium and oxygen silicon-based layers,respectively, are separated spatially by a predominately silicontransition layer which is deficient in both erbium and oxygen.Permutations of the preceding can be grown in order to gain the highestcompromise between epitaxial structural ordering for low defect densityand optical activation of the rare-earth ion.

[0059] Photonic device 10 can have at least one spacer layer 18 betweentwo adjacent repeating units 14. Additionally, a spacer layer 18 can bepositioned between more than one pair of adjacent repeating units 14,including all adjacent repeating units 14. The spacer layer is used toimprove the structural quality, symmetry, optical quality, or electronicquality of the superalattice. Additionally, superlattice 11 can bepositioned or grown on a substrate 20, including but not limited to asilicon substrate, or on a pseudo-substrate buffer layer 22 that has alattice constant which is different from a lattice constant of a bulksilicon substrate. Where a psuedo substrate is defined as thick layerwith low defect surface density that is grown over the substrate.

[0060] In one specific embodiment, superlattice 11 is grown on siliconsubstrate 20 along (001)- and (111), (211), (311), (411) and the likegrowth directions of the silicon substrate 20. The growth of the latticematched and/or lattice mismatched layers 12 can be epitaxially grown onsilicon substrate 20 or on a pseudo substrate 22 that can be a bulk orsuperlattice strained, or relaxed buffer layer. FIGS. 2(b) illustratessuperlattice 11 growth in the (111) direction. FIG. 2(c) illustrates anin-plane erbium/silicon active layer crystal structure without defectsgrown on a (111)-orientated surface.

[0061] In various embodiments, active region layer 16 has a latticelayer that is less than, the same as or equal to a lattice constant ofsilicon substrate 20 or pseudo-substrate buffer layer 22. It may bepreferred for active region layer 16 containing the rare-earth atoms tobe in a mechanically stressed state when grown epitaxially on siliconsubstrate 20 or pseudo substrate 22 by either tension, latticemismatching or compression. This reduces the defect density which inturn improves structural quality.

[0062] In certain embodiments, at least one layer in a repeating unit 14has a lattice constant that is sufficiently different from, (i) alattice constant of substrate 20 to have an opposite state of mechanicalstress or (ii) a lattice constant of pseudo-substrate buffer layer 22 tohave an opposite state of mechanical stress. In one embodiment, at leasttwo layers 12 of repeating units 14 have substantially equal andopposite mechanical strain states and, (i) each repeating unit 14 issubstantially lattice matched to substrate 20 or (ii) each repeatingunit 14 is substantially lattice matched to pseudo-substrate bufferlayer 22. Additionally, the crystal field of the superlattice can bemodified by a strain field induced by lattice mismatched layers in arepeating unit.

[0063] One example of strain balanced growth is an erbium containingsilicon-based layer 12 that exhibits a lattice constant smaller thanbulk silicon and is a lattice mismatched layer 12. Pseudomorphic growthof the lattice mismatched layer 12 can occur if the critical thicknessof an erbium silicide layer 12 is not exceeded. The erbium silicidelayer 12 is elastically deformed and under tensile strain.

[0064] The tensile strain can be balanced by the growth of an equal butopposite strain using, for example, a silicon germanium alloy where theamount of germanium is selected so the lattice constant is larger thanthat of bulk silicon and the layer thickness is tuned to counteract thetensile force of the erbium silicide layer with an equal but oppositecompressive force. If both of these layers 12 are below the criticallayer thickness and are stable, then the tensile and compressivelystrained layer pairs can be repeated N times, where N can be a verylarge number, for example up to 10,000, such that the total thickness ofthe resulting superlattice is up to three orders of magnitude largerthan the critical layer thickness of each of individual strained layers12. In this embodiment, the pseudomorphically grown strain balancedsuperlattice can be grown free of interfacial misfit dislocations andthus substantially free of surface states and trap level defects Thistype of strain balanced growth further reduces the segregation problemof epitaxial growth using impurities or rare-earth ions by periodicallytrapping the rare-earth ions below rare-earth deficient silicon-basedlayers. This method substantially solves the problem during epitaxialgrowth of layers involving segregating species- as they behave as asurfactant and are thus difficult to incorporate at high densities.

[0065] Repeating units 14 can have, (i) uniform layer constructions.,(ii) non-uniform layer constructions, (iii) thickness that vary as afunction of distance along a superlattice growth direction, (iv) layerchemical compositions and layer thickness that vary as a function ofdistance along a superlattice growth (v) at least two individual layers12, (vi) at least two individual layers 12 that have differentthickness, (vii) at least two individual layers 12 that are made ofdifferent compositions, (viii) at least three individual layers 12 thatare made of different compositions, (ix) a silicon layer 12 thatincludes rare earth ions, (x) a silicon germanium layer 12, (xi) asilicon oxide layer 12, (xii) an oxygen-doped silicon layer 12, (xiii) arare earth silicide layer 12, (xiv) a rare earth silicon germaniumlayer, (xv) an electrically doped p- or n-type layer 12 or (xvi)hydrogenated silicon 12, silicon oxynitride 12, hydrogenated siliconoxynitride, the same thickness and a thickness of the individual layersof the repeating units varies as a function of distance along asuperlattice growth direction.

[0066] At least a portion of repeating units 14 can have differentthickness, such superlattice 11 may be varied adjusted to controloptical or structural properties that vary in the growth process. Eachrepeating unit can be repeated N times, where N is a whole or partialinteger. Repeating units 14 cab be made of layers 12 that are thin. Inone embodiment, the thin layers 12 have a thickness of 1000 Å or lessand in another embodiment they are thin enough be non-bulk materiallayers 12.

[0067] The rare earth ion is preferably Er, Pr, Nd, Nd, Eu, Ho or Yb,and more preferably Er. In one embodiment, the rare earth ion has anenergy level that is determined by a geometric symmetry of a crystalfield produced by the constituent atomic arrangement and layer geometryof the superlattice 11.

[0068] The crystal field of photonic device 10 is configured to bevariable by altering the composition of the individual layers 12. Thisis achieved by the growth of several superlattices on top on each other,with each superlattice being a constant composition of repeating units14 but the number of repeating units 14 can vary in each superlattice.Alternatively, the crystal field of photonic device 10 can be configuredto be variable by altering the thickness and chemical composition ofindividual layers 12.

[0069] Active region layer 16 can include two or more different rareearth ions. This facilitates optical or electrical pumping of one ion byenergy transfer from the other ion. Additionally, active region layer 16can have a lattice constant substantially different to bulk silicon.Varying the lattice constant enables the electrical and opticalproperties to be adjusted and optimized.

[0070] Additionally, as illustrated in FIG. 2(d), the present inventionprovides intra-band transition of three-dimensionally configured quantumwell structures, e.g., a rare earth atomic transition can behave as atrue quantum-dot. This is contrasted with inter-band transitions betweenconduction and valence bands.

[0071] Referring to FIG. 3, optical device 10 has a core structure withalternating layers of silicon or silicon based compositions and rareearths. The rare earth can be capped with top and bottom layers 26 and28 that can be pure silicon layers. Electrical contacts 30 are appliedby implanting electrical dopants, including but not limited to rareearths or metals, to form low Schottky barrier suicides through top cap26 into a core of superlattice 11. Electrical contacts 30 can beimplanted. This implantation method is described in U.S. Pat. No.4,394,673, incorporated herein by reference. Erbium or other rare-earthsilicide is a suitable material for electrical contacts 30 because it isideal for high speed operation of optical gain/loss device 24 due to thesuperior ohmic contact resistance of the material. Such materialsinclude di-silicides, refractory metals and aluminum.

[0072] Optical gain/loss 24 can be a waveguide 24 for opticalpropagation by mode confinement through a refractive index change.Planar electrical devices using monolithic approaches involvingselective implantation can be utilized with waveguide 24 including butnot limited to, planar, or lateral, p-i-n, n-i-n or p-i-p. The in-planecarrier mobility of superlattice 11 is generally higher than verticaltransport in a direction perpendicular to layers 12. The presentinvention can also be a hybrid HBT or HFET device that providesmulti-electro-optic mode control. This can be achieved by incorporatingin-plane carrier extraction and injection using electrical contacts 30in conjunction with the electric fields that are produced above andbelow superlattice 11.

[0073] In one embodiment, illustrated in FIGS. 4(a) and 4(b), opticaldevice 10 is a switch 32. At least two optical gain devices 10 arecombined on a substrate 34. In FIG. 4, an input 36 is split and coupledto first and second gain/loss devices 24, that can be fabricated onsubstrate 34, and to two outputs 38. The split can cause loss. First andsecond gain/loss devices 38 are biased for gain or loss to produceamplification or attenuation. The basis of optical switch 32 uses thesimultaneous gain in one waveguide 24 and loss in the other to channellight through the former and not the latter. Splitting loss can beovercome in one or both waveguides 24.

[0074] In FIG. 4(b), an all optical multiplexer 40 includes two inputs36 input fibers that are optically routed to any of four outputs 38. TheFIG. 4(b) architecture can be scaled to include any number of inputs 36,outputs 38 and gain/loss devices 24 to form the fundamental fabric of anoptical network router and replaces optical-electrical-optical switchingwith an all optical architecture.

[0075] The FIG. 4(b) architecture can be scaled to an N×N opticalcross-connect (OXC) 42 illustrated in FIG. 5. In this embodiment,optical gain/loss devices 24 are curved rather than linear. Light iscoupled into and out of substrate 34 with a number of “N” conventionallinear waveguides 44 that crisscross substrate 34 to form an N×N grid.pattern. Linear waveguides 44 traverse in orthogonal directions whereeach direction is on a different level in the growth direction ofsubstrate 34. Each curved optical gain/loss device 24 joins theorthogonal linear waveguides 44. Light is coupled into and out of thelinear waveguides 44 and there is suppressed mode interference over theregion where curved gain/loss waveguides 24 join with and linearwaveguides 44. Optical gain/loss devices 24 overcome the lossesassociated with the suppressed mode coupling, and light is switchedbetween two orthogonal inputs when optical gain is initiated in curvedoptical loss/gain devices 24.

[0076] Referring now to FIG. 6, another embodiment of the presentinvention is a wavelength router/selector 46. In this embodiment,optical switches 32 form optical gates that are combined with passivewavelength routers of the type disclosed in U.S. Pat. No. 5,351,146,incorporated herein by reference. The passive wavelength router splitsthe various DWDM channels into separate waveguide gratings and thendirects them into appropriate output fibers.

[0077] Selection of an output port is determined by the choice ofwavelength used. Because multiple wavelengths may be used on each outputfiber, multiple simultaneous wavelength paths exist from each inputfiber. The wavelength routing properties of wavelength router/selector46 are periodic two ways. First, the spacing between frequencies foreach output selection are equal. Second, multiple free spectral rangesexist in the wavelength router/selector 46 so that the optical mutingproperty also repeats. This is achieved without power splitting lossbecause for a given wavelength constructive interference occurs only atthe waveguide or optical path designed for that wavelength, an all otherwaveguides cause destructive interference which prevents energy couplingto them.

[0078] The use of optical switches 32 enables wavelength router/selector46 to be a dynamically re-configurable, all-optical wavelength router.This eliminates the need for optical frequency changers at the interfacebetween the Level-1 and Level-2 networks or within the Level-2 networks.In current networks, this function is performed by multipleoptical-electrical-optical conversion which are expensive and bulky.

[0079] Referring now to FIG. 7, the present invention is also an opticalreceiver 48 where photons are converted into electrons. Optical receiverincludes superlattice 11 positioned between a p-doped layer 50 and ann-doped layer 52 which can both be made substantially of silicon.Electrodes 54 and 56 are coupled to p-doped layer 50 and n-doped layer52. Electrodes 54 and 56, in combination with other circuit elements,provide biasing, small-signal amplification and noise filtering.Superlattice 11 can be integrally formed with substrate 20 or pseudosubstrate 22. Additional elements can be integrated with substrate 20 orpseudo substrate 22. This level of integration enables optimum speed andminimal noise, giving the best signal to noise ratio and excellentdetection characteristics.

[0080] The present invention is also a tunable or non- laser such as anedge emitting laser 58 of FIG. 8 or a VCSEL 60 of FIG. 9.

[0081] Edge emitting laser 58 includes superlattice 11 in the plane ofsubstrate 20 or pseudo-substrate 22. Edge-emitting laser 58 includeselectrodes to excite superlattice 11, lower and upper optical waveguidecladding layers, a high mobility silicon layer used for electronictransistor construction, n-type well field effect transistors (FET), afield effect, gate oxide layer, a silicon oxide isolation layer, andlateral oxidation of silicon layers that are used for electronic andsuperlattice 11 isolation.

[0082] With VCSEL 60, light travels in superlattice 11 orthogonal to theplane of substrate 20 or pseudo substrate 22. First and second mirrors62 and 64 define a resonant cavity. VCSEL 60 includes electrodes toexcite superlattice 11, lower and upper optical waveguide claddinglayers, a high mobility silicon layer used for electronic transistorconstruction, n-type well field effect transistors (FET), a fieldeffect, gate oxide layer, a silicon oxide isolation layer, lateraloxidation of silicon layers that are used for electronic andsuperlattice 11 isolation, and a micromachines silicon micro-lens arrayin substrate 20.

[0083] Reflectors 62 and 64 can be grown as Bragg gratings, or producedby cleaving facets on the ends of substrate 20 or pseudo-substrate 22.This cleaving process is described in U.S. Pat. No. 5,719, 077,incorporated herein by reference. The output wavelength of the lasers 58and 60 can be tuned by varying the repeating unit 14 of superlattice 11,which changes the crystal field and hence the transition energy of thelaser transition. Bragg elements Acting either as an integral cavitymirror or external feedback element, can be fabricated at the output endof lasers 58 and 60 to provide feedback which limits and controlslinewidth. Tuning and bandwidth can be controlled by varying period ofrepeating unit 14.

[0084]FIG. 8 illustrates one embodiment of the integration of arare-earth crystal field superlattice 11 grown epitaxially on substrate20 and pseudo-substrate 22. Following the completion of superlattice 11a spacer layer 65 is grown to isolate a high mobility silicon layer thatis suitable for Si CMOS VLSI. This example of an MBE grown epitaxialcompound silicon-based substrate 20 or pseudo-substrate 22 can then beprocessed to form ion-implantation doped regions, electrical contacts tothe doped ion-implanted regions, silicon oxide field effect gate regionsand dielectric isolation regions

[0085] The optical gain material is located beneath the final highmobility silicon layer. Optical gain regions can be electricallyisolated using ion-implantation or deep trenches. The optical mode ofplanar waveguide photonic circuits can be designed as ridge-type, buriedcore, stripe or implant diffused geometries. Relative temperaturestability of the emission wavelengths of the gain spectrum allow highfrequency and power silicon electronics to be operated simultaneously.

[0086] The optical waveguide mode can be confined in the core region byappropriate growth of suitable lower cladding material. This can beachieved for the core and cladding layers by selectively altering thelayer refractive index via impurity doping; or via the use of silicongermanium alloys or the use of silicon oxide buried layers. The latterexample, can be implemented for the lower cladding oxide layers usingepi-ready separation by oxygen implantation (SIMOX) silicon wafers,silicon-on-insulator (SOI) or silicon-on-sapphire (SOS) startingsubstrates 20 or pseudo-substrates 22.

[0087] With VCSEL 60, very few layers 12 are required to form mirrors 62and 64 because the index contrast between layers 12 can be made verylarge. With the use of a silicon-based material, the refractive indexdifference between silicon -based DBR mirror 62 and buffer is muchhigher and the required number of layers 12 for mirrors 62 and 64 can beas low as two to ten.

[0088] VCSEL 60 uses superlattice 11 as the gain medium. The cavity isformed by a high reflectivity quarter wave pair Bragg mirror 62 andoutput coupling quarter wave Bragg reflector 64. The multi period highreflectivity mirror 64 can be grown/fabricated preceding superlattice 11or as part of the final processing steps of the CMOS compatible process.The backside of substrate 20 can be micro-machined into arrays ofmicro-lenses or optical fiber receptacles. This process would allowsimple alignment of optical-interconnects from chip-to-chip orfiber-to-chip.

[0089] Additionally, a wavelength tuning member, sensor and control loopcan each be coupled to lasers 58 and 60. In response to a detectedchange in temperature or optical power the control loop sends anadjustment signal to the tuning member and the tuning member adjusts avoltage or current supplied to laser 58 and 60 to provide a controlledoutput beam of selected wavelength.

[0090] The period of repeating unit 14 can be chirped across substrate20 or pseudo substrate 22 as shown in FIG. 10. This provides acontrolled variation of wavelength based on the position on substrate 20or pseudo substrate 22. The crystal field varies with physical periodand composition of the superlattice, thus varying the period in acontinuous fashion (i.e., chirp) causes a continuous shift in crystalfield and therefore laser output wavelength. Multiple lasers withdifferent wavelengths, separated by discrete steps, can be produced on asingle substrate 20 or pseudo substrate 22. This provides discrete steptuning from a single component with internal circuitry simply byelectronic selection of the appropriate wavelength laser. that can becreated on the same substrate 20 or pseudo substrate 22 using standardVLSI techniques. In this manner, lasers 58 and 60, and their electronicswitching fabric, reside on the a single substrate 20 or pseudosubstrate 22. The appropriate laser wavelength is then selected byelectrical input signals which on-board chip components decode, or bysimple external wiring which can be grown as selective area growthMOCVD. With this concept, superlattice 11 can be initially grown as astructure that changes its layer 12 thickness uniformly across across-sectional area. This is useful for a transmitter in a DWDM system.

[0091] As illustrated in FIG. 11, superlattice 11 can also be chirped byvarying the thickness of the alternating rare-earth layers. In thisembodiment, both the bandwidth and center wavelength are controlled.

[0092] Referring now to FIG. 12, optical receiver 48 can be combinedwith laser 58 or 60 on the same substrate 20 or pseudo substrate 22 toform a monolithic transceiver 66. Circuitry 68 is also fabricated on thesame substrate 20 or pseudo substrate. Circuitry 68 can include anelectrical amplifier, signal processor, diode laser driver and the like.Circuitry 68 can be used to, bias optical receiver 48 and lasers 58, 60,amplify the photons detected by optical receiver 48, drive and modulatelaser 58 and 60, and the like. Circuitry 68 enables conversion ofphotons into electrons and enable electrons to drive and modulate laser58 and 60. Monolithic transceiver 66 can be used to replace the discreteelements in a standard telecommunications router.

[0093] In another embodiment, illustrated in FIG. 13, a monolithicoptical router 70 includes a plurality of lasers 58 and 60 and aplurality of optical receivers 48 all combined on a single substrate 20or pseudo substrate 22 with circuitry 72. Circuitry 72 biases theplurality of lasers 58 and 60 and optical receivers 48 to amplify thephotons that are detected and then drive and modulate the plurality oflasers 58 and 60. An additional set of circuit elements forms anelectrical switching fabric 74 that enables signals generated by one ormore of the optical receivers 48 to be routed to any laser 58 and 60.Monolithic optical router 70 enables optical signals on any one of aninput to be switched to any one of the outputs.

[0094] Another embodiment of the present invention, illustrated in FIG.14, is a wavelength converter 76 with at least two optical loss/gaindevices 24. of Data is carried via modulated on an optical signal at afirst wavelength, and input to the waveguide. A second wavelength isinput to the waveguide and mixes with the first wavelength. Themodulation from the first wavelength is transferred to the secondwavelength by cross-gain or cross-phase modulation. The traveling wave(single pass) gain receives simultaneously the modulated optical signalat the first wavelength and the second optical signal at the desiredwavelength. The first optical signal affects the gain of the travelingwave gain as seen by the second optical signal so as to impress arepresentation of variations in the envelope of the first optical signalonto the second optical signal. The basic structure is that of aMach-Zehnder interferometer with cross-phase modulation.

[0095]FIG. 15 illustrates a parametric nonlinear optical element 78embodiment of the present invention. Superlattice 11 forms a firstwaveguide 80, which can be optical loss/gain device 24, that isoptimized for optical gain an a predetermined pump wavelength, e.g. 1540nm. Additional superlattice structures 11 form second and thirdwaveguides 82 and 84 on opposite sides of first waveguide 80. Second andthird waveguides 82 and 84 are optimized for side-band frequenciesadjacent to the pump wavelength, including but not limited to 1650 nmand 1450 nm.

[0096] Second and third waveguides 82 and 84 are positioned sufficientlyclose (i.e., close to the wavelength of the light; e.g. 1.5-3 um for1500 nm light) as to achieve evanescent wave-coupling to first waveguide80 in order to allow coupling. When the pump wavelength propagatesthrough first waveguide 80 sideband wavelengths are driven in second andthird waveguides 82 and 84, and energy flows from the pump wavelength tothe sideband wavelengths. This creates a passive wavelength converterthrough nonlinear optical coupling. Subsequent to the conversion,additional optical loss/gain devices 24 can be placed in order tosuppress the residual pump and enhance either or both of the sidebandwavelengths. In this embodiment, parametric nonlinear optical element 78becomes an active element which switches between adjacent DWDM channelsto allow wavelength routing.

[0097] The present invention is also a quasi-phase matched nonlinearelement 86, as shown in FIG. 16. In this embodiment, superlattice 11 isgrown with a periodic variation in refractive index in order to inducegain at signal or idler frequencies of the input beam to quasi-phasematched nonlinear element 86. The periodic variation is chosen toachieve quasi-phase-matching through periodic refractive index variationat the appropriate frequency. In this embodiment, the active regionlayers 16 act as a nonlinear optical crystal whose gain can beelectrically enhanced. The signal and idler frequencies are those of anoptical parametric oscillator (OPO) in the 1000-2000 nmtelecommunications band. Acting as an OPO, the active region layers 16can shift an input DWDM wavelength to another wavelength with the energydifference carried off by the idler wavelength.

[0098] In another embodiment, illustrated in FIG. 17, multiple opticalloss/gain devices 24 gain/loss elements are used in an all opticaladd-drop multiplexer (OADM) 88. OADM 88 includes an opticaldemultiplexer 90 that splits an input WDM signal into individual opticalsignals, leading to respective 2×2 switches. Each switch has anotherinput that originates from a plurality of add lines and selects one ofits inputs to be dropped and the other to continue along a main signalpath.

[0099] The retained signals may be modulated and attenuated prior tobeing tapped and finally multiplexed together by a WDM multiplexer 92.The tapped signals are opto-electronically converted and fed back to acontroller, which can include controller software, that controls theswitching, modulation and attenuation. This permits remote control ofOADM 88 functions by encoding instructions for the controller into alow-frequency dither signal that is embedded within the individualoptical signals. OADM 88 can, in real time, be instructed to reroutetraffic, dynamically equalize or otherwise change optical channel powerlevels, and add or remove dither. A specific optical channel may bereserved for control purposes, allowing a network administrator to “login” to OADM 88 and override the controller software algorithm.Optionally, the optical signals can be tapped upon entry to OADM 88. Adi-directional OADM can be constructed from two unidirectional OADM's 88that can share the same controller. Additionally, a single, generalmulti-input multi-output switch can be used to provide an arbitrarymapping between individual input and output optical signals.

[0100] Alternatively, as shown in FIG. 18, the present invention is alsoa two-dimensional photonic bandgap (2D-PBG) structure 94 implanted inthe output path of the input beam or waveguide Bandgap structure 94includes superlattice 11 with periodic variation, and repeating units 14of bandgap structure 94 are selected to optimize the diffraction oflight. Bandgap structure 94 consists of an array of predominatelycylindrical ion-implantation disordering doped or physically etchedregions either within or external to the superlattice. orthogonal to theplane of substrate 20 or pseudo substrate 22 which act as a diffractiongrating.

[0101] Scatter radiation emitted form bandgap structure 94 fans out atangles with the angle of diffraction being determined by the wavelengthof the radiation. Thus the photonic bandgap structure acts as adiffraction grating but with substantially higher efficiency andcustomized dispersion. . Unlike a diffraction grating, bandgap structure94 directs spatially resolved wavelengths in the forward direction. Thisis advantageous for highly dispersive, integrated wavelength selectiveopto-electronic structures. Bandgap structure 94 can be an active DWDMfilter that separates various wavelengths. The separated wavelengths canthen be coupled into their own waveguides. Each waveguide can then becoupled to a switch 32.

[0102] In another embodiment, illustrated in FIG. 19, the presentinvention is a selectable wavelength add/drop multiplexer 96 that has aconcentric ring waveguide 98 fabricated in substrate 20 orpseudo-substrate 22 to form a “Light Coral” of the type described byNanovation, “The Micro revolution”, Technology Review” July-August 2000,incorporated herein by reference, in which light of a frequency resonantwith ring waveguide 98 is selectively coupled out of one verticalwaveguide and into the other vertical waveguide, via ring waveguide 98which includes a superlattice 11 with optical gain/loss device 24 toenhances or suppress the wavelength coupled into ring waveguide 98. Theaddition of optical gain/loss device 24 makes ring waveguide 98 act asselectable wavelength add/drop multiplexer 96.

[0103] The present invention can also be an actively equalized arraywaveguide grating shown in FIG. 6. By combining the properties ofoptical gain and detection in devices that include superlattice IIprovides integrated optical monitoring devices and systems. Inputwavelength division multiplexed signals are separated into theconstituent individual wavelengths by the arrayed waveguide grating(AWG) and propagate through individual waveguides. Superlattice 11 canattenuate or amplify each of these signals independently, therebyproviding dynamic spectral gain control and equalization. For example,an AWG can include superlattice 11. Waveguides 24 of the AWG can havemultiple electrodes that are configured to either provide control of thegain or a photodetection of the propagating optical signal. Activefeedback of the gain sections can be controlled by monitoring theoptical power in each of the waveguides and thus provide the capabilityof actively equalizing the AWG.

[0104] A further embodiment of the present invention is an opticalintegrated circuit 100, illustrated in FIG. 20 that includes many of theFIG. 1-FIG. 19 devices and embodiments. Such a circuit combines photonsand electrons into a single substrate, fabricated by a single process,and enables both optical and electrical gain and control to beintegrated together. Full VLSI functionality including all electricalfunctions currently employed in silicon VLSI such as memory, switching,gain, computation, fuzzy logic, error checking, and restoration.Likewise, all optical functions currently achieved by discrete passiveand active components, such as optical switching, wavelength filtering,optical mixing, amplification, loss, MUX/DEMUX, detection, modulation,laser output, LED, and nonlinear effects, can also be integrated throughsilicon VLSI.

[0105] While embodiments of the invention have been illustrated anddescribed, it is not intended that these embodiments illustrate anddescribe all possible forms of the invention. Rather, the words used inthe specification are words of description rather than limitation, andit is understood that various changes may be made without departing fromthe spirit and scope of the invention.

What is claimed is:
 1. A photonic device, comprising: a siliconsemiconductor based superlattice that includes a plurality of layersthat form a plurality of repeating units, wherein at least one of thelayers in the repeating unit is an optically active layer with at leastone species of rare earth ion and at least two units in a repeating unithave different thicknesses.
 2. The device of claim 1, wherein each layerin the plurality of layers is a pure crystalline structure.
 3. Thedevice of claim 1, wherein the rare earth ion is present with a densityof at least 10¹⁸ ions per cubic cm.
 4. The device of claim 1, furthercomprising: one or more cladding layers coupled to the superlatticeconfigured to guide and propagate an optical mode that overlaps at leasta portion of the superlattice.
 5. The device of claim 1, furthercomprising: first and second electrodes , wherein at least a portion ofthe superlattice is positioned between the first and second electrodes.6. The device of claim 1, further comprising: a least one electrode thatextends from an exterior of the superlattice to an interior of thesuperlattice.
 7. The device of claim 1, further comprising: at least oneelectrically doped p- or n-type layer coupled to the superlattice. 8.The device of claim 1, wherein the optically active layer is sandwichedbetween doped p- or n-type layers.
 9. The device of claim 1, furthercomprising: a mode size converter configured to be coupled to an opticalfiber and the superlattice.
 10. The device of claim 1, wherein the modesize converter is a tapered waveguide structure.
 11. The device of claim1, wherein the repeating units are periodic.
 12. The device of claim 1,wherein the repeating units have uniform layer constructions.
 13. Thedevice of claim 1, wherein the superlattice structure is selected tocreate a global crystal field that interacts with the local crystalfield of the constituent host layers to produce a pre-determined opticalspectrum of the structure.
 14. The device of claim 1, wherein a crystalfield of the device is configured to be spatially variable by alteringcomposition of layers.
 15. The device of claim 1, wherein a compositionof the repeating units varies as a function of distance along asuperlattice growth.
 16. The device of claim 1, wherein at least one ofthe layers is amorphous.
 17. The device of claim 1, wherein at least aportion of the active region layer is a narrow band gap semiconductorrelative to other layers in a repeating unit.
 18. The device of claim 1,wherein at least a portion of the active region layer is a wide band gapsemiconductor relative to other layers in a repeating unit.
 19. Thedevice of claim 1, further comprising at least one spacer layer betweentwo adjacent repeating units.
 20. The device of claim 19, wherein thespacer layer varies in thickness along a growth direction.
 21. Thedevice of claim 1, wherein the repeating units includes ultra-thinlayers.
 22. The device of claim 133, wherein the ultra-thin layers havea thickness of 1000 Å or less.
 23. The device of claim 133, wherein theultra- layers are thin enough to be non-bulk material layers.
 24. Thedevice of claim 1, wherein each repeating unit has two or more layers.25. The device of claim 1, wherein each repeating unit is repeated Ntimes, where N is a whole or partial integer of monolayers.
 26. Thedevice of claim 1, wherein each repeating unit has at least two layersmade with different compositions.
 27. The device of claim 1, whereineach repeating unit has at least two layers with different thicknesses.28. The device of claim 1, wherein each repeating unit has three layersmade of with different compositions.
 29. The device of claim 1, whereineach repeating unit has a silicon oxide layer.
 30. The device of claim1, wherein each repeating unit has an oxygen-doped silicon layer. 31.The device of claim 1, wherein each repeating unit includes anelectrically doped p- or n-type layer.
 32. The device of claim 1,further comprising: at least one crystal growth modifier M included inat least one crystalline layer of each repeating unit in the form ofSiMx, where x is less than
 1. 33. The device of claim 32, wherein thegrowth modifier M is a crystalline compound comprising a rare-earth Rand M is at least one of C, H, O, N, P, As, B, Sb, Co, Ni, Ir, Sn and Pbin the form RxMy.
 34. The device of claim 1, wherein the rare earth ionis selected from at least one of Er, Pr, Nd, Eu, Ho, Pm, Tb, Sm, Tm andYb.
 35. The device of claim 1, wherein the rare earth ion is Er.
 36. Thedevice of claim 1, wherein the multi-layer silicon based superlattice ispositioned on a silicon substrate.
 37. The device of claim 1, whereinthe multi-layer silicon based superlattice is grown on a siliconsubstrate.
 38. The device of claim 1, wherein the multi-layer siliconbased superlattice is grown on an (001)-oriented surface of the siliconsubstrate.
 39. The device of claim 1, wherein the multi-layer siliconbased superlattice is grown on a (111)-oriented surface of the siliconsubstrate.
 40. The device of claim 1, wherein the multi-layer siliconbased superlattice is grown on at least one h, k and l-oriented surfaceof the silicon substratem wherein h, k, and l are sets of integers thatare crystallographic Miller indices notation.
 41. The device of claim 1,wherein the multi-layer silicon based superlattice is grown on one of ageometrically and compositionally patterned silicon substrate.
 42. Thedevice of claim 1, wherein the multi-layer silicon based superlattice isdeposited in a superlattice growth direction and has a laterally orderedstructure substantially perpendicular to a growth direction.
 43. Thedevice of claim 1, wherein the multi-layer silicon based superlattice isdeposited in a superlattice growth direction and has a laterally orderedstructure substantially perpendicular to a growth direction.
 44. Thedevice of claim 1, wherein the multi-layer silicon based superlattice isgrown on a silicon-on-insulator wafer.
 45. The device of claim 1,wherein the active region layer has a lattice constant that is less thana lattice constant of an underlying bulk silicon substrate.
 46. Thedevice of claim 1, wherein the active region layer has a latticeconstant that is less than a lattice constant of a on a pseudo-substratebuffer layer with a lattice constant that is different from a latticeconstant of an underlying bulk silicon substrate.
 47. The device ofclaim 1, wherein the active region layer has a lattice constant that isequal to a lattice constant of an underlying bulk silicon substrate. 48.The device of claim 1, wherein the active region layer has a latticeconstant that is equal to a lattice constant of a on a pseudo-substratebuffer layer with a lattice constant that is different from a latticeconstant of an underlying bulk silicon substrate.
 49. The device ofclaim 1, wherein the active region layer has a lattice constant that isgreater than a lattice constant of an underlying bulk silicon substrate.50. The device of claim 1, wherein the active region layer has a latticeconstant that is greater than a lattice constant of a on apseudo-substrate buffer layer with a lattice constant that is differentfrom a lattice constant of an underlying bulk silicon substrate.
 51. Thedevice of claim 37, wherein at least one layer in a repeating unit has alattice constant that is sufficiently different from a lattice constantof the substrate to be substantially in a state of elastic mechanicalstress.
 52. The device of claim 37, wherein at least two of layers ofrepeating units have substantially equal and opposite mechanical strainenergy and strain states and each repeating unit is substantiallylattice matched to the silicon substrate.
 53. The device of claim 37,wherein at least two of layers of repeating units have substantiallyequal and opposite mechanical energy and strain states and eachrepeating unit is substantially lattice matched to the pseudo-substratebuffer layer.
 54. The device of claim 14, wherein the crystal field ismodified by a strain field induced by lattice mismatched layers in arepeating unit.
 55. A photonic device, comprising: a siliconsemiconductor based superlattice that includes a plurality of layersthat form a plurality of repeating units, wherein at least one of thelayers in the repeating unit is an optically active layer with at leastone species of rare earth ion and at least two units in a repeating unitare made of different compositions.
 56. The device of claim 55, whereineach layer in the plurality of layers is a pure crystalline structure.57. The device of claim 55, wherein the rare earth ion is present with adensity of at least 10¹⁸ ions per cubic cm.
 58. The device of claim 55,further comprising: one or more cladding layers coupled to thesuperlattice configured to guide and propagate an optical mode thatoverlaps at least a portion of the superlattice.
 59. The device of claim55, further comprising: first and second electrodes , wherein at least aportion of the superlattice is positioned between the first and secondelectrodes.
 60. The device of claim 55, further comprising: a least oneelectrode that extends from an exterior of the superlattice to aninterior of the superlattice.
 61. The device of claim 55, furthercomprising: at least one electrically doped p- or n-type layer coupledto the superlattice.
 62. The device of claim 55, wherein the opticallyactive layer is sandwiched between doped p- or n-type layers.
 63. Thedevice of claim 55, further comprising: a mode size converter configuredto be coupled to an optical fiber and the superlattice.
 64. The deviceof claim 55, wherein the mode size converter is a tapered waveguidestructure.
 65. The device of claim 55, wherein the repeating units areperiodic.
 66. The device of claim 55, wherein the repeating units haveuniform layer constructions.
 67. The device of claim 55, wherein thesuperlattice structure is selected to create a global crystal field thatinteracts with the local crystal field of the constituent host layers toproduce a pre-determined optical spectrum of the structure.
 68. Thedevice of claim 55, wherein a crystal field of the device is configuredto be spatially variable by altering composition of layers.
 69. Thedevice of claim 55, wherein a composition of the repeating units variesas a function of distance along a superlattice growth.
 70. The device ofclaim 55, wherein at least one of the layers is amorphous.
 71. Thedevice of claim 55, wherein at least a portion of the active regionlayer is a narrow band gap semiconductor relative to other layers in arepeating unit.
 72. The device of claim 55, wherein at least a portionof the active region layer is a wide band gap semiconductor relative toother layers in a repeating unit.
 73. The device of claim 55, furthercomprising at least one spacer layer between two adjacent repeatingunits.
 74. The device of claim 73, wherein the spacer layer varies inthickness along a growth direction.
 75. The device of claim 55, whereinthe repeating units includes ultra-thin layers.
 76. The device of claim75, wherein the ultra-thin layers have a thickness of 1000 Å or less.77. The device of claim 75, wherein the ultra- layers are thin enough tobe non-bulk material layers.
 78. The device of claim 55, wherein eachrepeating unit has two or more layers.
 79. The device of claim 55,wherein each repeating unit is repeated N times, where N is a whole orpartial integer of monolayers.
 80. The device of claim 55, wherein eachrepeating unit has at least two layers made with different compositions.81. The device of claim 55, wherein each repeating unit has at least twolayers with different thicknesses.
 82. The device of claim 55, whereineach repeating unit has three layers made of with differentcompositions.
 83. The device of claim 55, wherein each repeating unithas a silicon oxide layer.
 84. The device of claim 55, wherein eachrepeating unit has an oxygen-doped silicon layer.
 85. The device ofclaim 55, wherein each repeating unit includes an electrically doped p-or n-type layer.
 86. The device of claim 55, further comprising: atleast one crystal growth modifier M included in at least one crystallinelayer of each repeating unit in the form of SiMx, where x is lessthan
 1. 87. The device of claim 85, wherein the growth modifier M is acrystalline compound comprising a rare-earth R and M is at least one ofC, H, O, N, P, As, B, Sb, Co, Ni, Ir, Sn and Pb in the form RxMy. 88.The device of claim 55, wherein the rare earth ion is selected from atleast one of Er, Pr, Nd, Eu, Ho, Pm, Tb, Sm, Tm and Yb.
 89. The deviceof claim 55, wherein the rare earth ion is Er.
 90. The device of claim55, wherein the multi-layer silicon based superlattice is positioned ona silicon substrate.
 91. The device of claim 55, wherein the multi-layersilicon based superlattice is grown on a silicon substrate.
 92. Thedevice of claim 55, wherein the multi-layer silicon based superlatticeis grown on an (001)-oriented surface of the silicon substrate.
 93. Thedevice of claim 55, wherein the multi-layer silicon based superlatticeis grown on a (111)-oriented surface of the silicon substrate.
 94. Thedevice of claim 55, wherein the multi-layer silicon based superlatticeis grown on at least one h, k and l-oriented surface of the siliconsubstratem wherein h, k, and l are sets of integers that arecrystallographic Miller indices notation.
 95. The device of claim 55,wherein the multi-layer silicon based superlattice is grown on one of ageometrically and compositionally patterned silicon substrate.
 96. Thedevice of claim 55, wherein the multi-layer silicon based superlatticeis deposited in a superlattice growth direction and has a laterallyordered structure substantially perpendicular to a growth direction. 97.The device of claim 55, wherein the multi-layer silicon basedsuperlattice is deposited in a superlattice growth direction and has alaterally ordered structure substantially perpendicular to a growthdirection.
 98. The device of claim 55, wherein the multi-layer siliconbased superlattice is grown on a silicon-on-insulator wafer.
 99. Thedevice of claim 55, wherein the active region layer has a latticeconstant that is less than a lattice constant of an underlying bulksilicon substrate.
 100. The device of claim 55, wherein the activeregion layer has a lattice constant that is less than a lattice constantof a on a pseudo-substrate buffer layer with a lattice constant that isdifferent from a lattice constant of an underlying bulk siliconsubstrate.
 101. The device of claim 55, wherein the active region layerhas a lattice constant that is equal to a lattice constant of anunderlying bulk silicon substrate.
 102. The device of claim 55, whereinthe active region layer has a lattice constant that is equal to alattice constant of a on a pseudo-substrate buffer layer with a latticeconstant that is different from a lattice constant of an underlying bulksilicon substrate.
 103. The device of claim 55, wherein the activeregion layer has a lattice constant that is greater than a latticeconstant of an underlying bulk silicon substrate.
 104. The device ofclaim 55, wherein the active region layer has a lattice constant that isgreater than a lattice constant of a on a pseudo-substrate buffer layerwith a lattice constant that is different from a lattice constant of anunderlying bulk silicon substrate.
 105. The device of claim 91, whereinat least one layer in a repeating unit has a lattice constant that issufficiently different from a lattice constant of the substrate to besubstantially in a state of elastic mechanical stress.
 106. The deviceof claim 91, wherein at least two of layers of repeating units havesubstantially equal and opposite mechanical strain energy and strainstates and each repeating unit is substantially lattice matched to thesilicon substrate.
 107. The device of claim 91, wherein at least two oflayers of repeating units have substantially equal and oppositemechanical energy and strain states and each repeating unit issubstantially lattice matched to the pseudo-substrate buffer layer. 108.The device of claim 91, wherein the crystal field is modified by astrain field induced by lattice mismatched layers in a repeating unit.